Subject: Building of arch/arm/plat-mxc/ssi-fiq.S failed w/ THUMB2 enabled?

From: [email-masked] (Dave Martin)
Date: Fri, 20 Jan 2012 15:02:51 +0000

On Fri, Jan 20, 2012 at 11:56:06AM +0000, Russell King - ARM Linux wrote:
> On Fri, Dec 02, 2011 at 01:39:11PM +0000, Dave Martin wrote:
> > Is this code still used on ARMv7 and above?  FIQ is not normally
> > available for Linux interrupts on hardware which makes use of the
> > TrustZone security extensions.  Plus, on modern hardware with a deep
> > memory hierarchy, FIQ is may not be all that "fast" either, due to
> > cache/TLB effects.
> 
> It's worth pointing out that people end up using FIQs for certain things
> because the hardware requires you to do it.  So if a platform is using
> them, they're probably not doing it out of choice, but are doing it
> because it's a baseline requirement to get something working.

Agreed -- but I'm wondering whether this code is actually non-relevant
to newer platforms, and is only being built at all because of a
non-relevant driver being included in mx5_defconfig, or due to some
Kconfig anomaly.

If this is really non-relevant to any >= v7 platform, we just need
for fix Kconfig : this code should never ever be built into a Thumb-2
kernel in that case.

Unfotunately I don't have the i.MX hardware knowledge to answer that
"if" though... it's just a hunch on my part.

One of the i.MX guys will have to comment on that.

Cheers
---Dave